He also transferred a 42% stake in the company to her sister, Katharina, who at 20 is the second-youngest billionaire in the world. She's also worth $1.2 billion.

Alexandra was only recently confirmed as the world's youngest billionaire because the Norwegian government publishes the tax returns of people over 17.

But despite her affluent upbringing in one of the best-known Norwegian families, she isn't just any rich kid. Alexandra is already an accomplished horse rider, winning several massive competitions in dressage.

Her parents also taught her to be humble and to save. So even though she is worth over a billion dollars, she actually saved her pocket money during her younger years and drove only secondhand cars.

Alexandra Andresen was born in 1997 in Oslo, Norway, where she was also primarily raised.

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Her father is Johan Andresen, son of industrialist Johan Henrik Andresen and Marianne Ebba Therese Bielke.

Twitter/Johan Andresen

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The Andresen family made their money from their tobacco brand, Tiedemanns, which the clan held until 2005 under Ferd. Today, Ferd mainly runs hedge funds. It also is an active investor on the Nordic stock exchange and has private-equity investments.

Ferd

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She was also raised by her mother, Kristin. Here is her mother when she was younger.

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She has one sister, Katharina, who is a year older, making her the second-youngest billionaire in the world.

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Their house and land was always filled with animals. On Instagram, Alexandra said: "We used to bring our ponies, Pinocchio (pinto) and Spike (brown), to an island where we had a summerhouse. They would walk free on our property."

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They have also had several dogs, including Bella.

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So it was natural that they found an affinity for horses and other animals from an early age.

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The family's dogs even follow her around when she's riding her horse.

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Her father sold the family's stake in the tobacco business to Skandinavisk Tobakskompagni for nearly $500 million in 2005.

Two years later, Johan transferred a 42% stake of Ferd each to Alexandra and Katharina. Alexandra was 10.

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But Johan still controls the company, and Alexandra's and Katharina's wealth has become public only because Norway publishes the tax returns of any person over 17.

EY Norge/YouTube

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Alexandra picked up horseback riding at a young age, and in recent years she has forged a career as a professional dressage competitor.

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Alexandra is a three-time junior Norwegian dressage champion. Here she is receiving the AEG Galla 2014 Best Achievement of the Year Award.

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She is now sponsored by Kingsland, an equestrian company, for her dressage competitions.

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While Alexandra and Katharina have inherited enormous fortunes from Ferd, their father insists that they won't be forced to help run the company in the future, he told Norwegian newspaper Aftenposten in 2015.

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So far, Katharina appears the more likely of the two sisters to work at Ferd, having completed an internship at the family company. Katharina is now studying social sciences at Amsterdam University College.

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Meanwhile, Alexandra is still unsure about the future. She said in an interview on Ferd's website: "I feel a great responsibility. In a way I think that I have not made ​​me deserving of this, while I want to help develop Ferd and make it even better. Finding a way to give something back, I think is difficult."

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"The fact that my family has resources has given me many opportunities, especially in the riding, because it requires a lot of capital. But it is not enough to have money to succeed," Alexandra added.

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But in another interview last year with Eurodressage magazine, she said: "This is what I want to do for the rest of my life — ride!"

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Though she has been aware of her wealth from a young age, Alexandra told Ferd's corporate magazine that her parents always taught the sisters to save pocket money and made them drive secondhand cars, according to The Telegraph.

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Apart from the horse-riding circuit, she lives a relatively low-key life.

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Though she does like the occasional holiday.

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And she also brings her friends to red-carpet events.

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She's close to her mother, who shares her love of horse riding.

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Alexandra also has a 24-year-old boyfriend, Joachim Tollefsen, a professional mixed-martial-arts fighter from Norway.

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But the love of her life is her horse riding, which dominates her Instagram account and all her social-media activity.